Emulsifier-free finely disperse systems of the water-in-oil type

ABSTRACT

Pickering emulsions, which are finely disperse systems of the water-in-oil type, comprising 
     (1) an oil phase, 
     (2) a water phase, 
     (3) at least one type of microfine particles which 
     a) have an average particle size of less than 200 nm, which 
     b) display both hydrophilic and lipophilic properties, i.e. which have amphiphilic character, and are dispersible both in water and in oil and which 
     c) have optionally been coated on the surface, 
     (4) at least one hydrocolloid and 
     (5) at most 0.5% by weight of one or more emulsifiers.

The present invention relates to emulsifier-free finely disperse systemsof the water-in-oil type, preferably as cosmetic or dermatologicalpreparations.

Emulsions are generally taken to mean heterogeneous systems whichconsist of two liquids which are immiscible or have only limitedmiscibility with one another, which are usually referred to as phases.In an emulsion, one of the two liquids is dispersed in the form of veryfine droplets in the other liquid.

If the two liquids are water and oil and if oil droplets are finelydispersed in water, then this is an oil-in-water emulsion (OMI emulsion,e.g. milk). The basic character of an O/W emulsion is defined by thewater. In a water-in-oil emulsion (W/O emulsion, e.g. butter),. theprinciple is reversed, the basic character here being determined by theoil.

In order to achieve permanent dispersion of one liquid in another,emulsions in the traditional sense require the addition of aninterface-active substance (emulsifier). Emulsifiers have an amphiphilicmolecular structure, consisting of a polar (hydrophilic) and a nonpolar(lipophilic) molecular moiety, which are spatially separate from oneanother. In simple emulsions, finely disperse droplets of one phase,surrounded by an emulsifier shell, (water droplets in W/O emulsions orlipid vesicles in O/W emulsions) are present in the second phase.Emulsifiers lower the interfacial tension between the phases bypositioning themselves at the interface between two liquids. At thephase boundary, they form oil/water interfacial films, which preventirreversible coalescence of the droplets. Emulsions are frequentlystabilized using emulsifier mixtures.

Traditional emulsifiers can, depending on their hydrophilic molecularmoiety, be divided into ionic (anionic, cationic and amphoteric) andnonionic:

The most well-known example of an anionic emulsifier is soap, which isusually the term used for the water-soluble sodium or potassium salts ofsaturated or unsaturated higher fatty acids.

Important examples of cationic emulsifiers are quaternary ammoniumcompounds.

The hydrophilic molecular moiety of nonionic emulsifiers frequentlyconsists of glycerol, polyglycerol, sorbitans, carbohydrates andpolyoxyethylene glycols, and, in most cases, is linked to the lipophilicmolecular moiety via ester and ether bonds. The lipophilic molecularmoiety usually consists of fatty alcohols, fatty acids or isofattyacids.

By varying the structure and the size of the polar and nonpolarmolecular moiety, the lipophilicity and hydrophilicity of emulsifierscan be varied within wide limits.

A decisive factor for the stability of an emulsion is the correct choiceof emulsifiers. The characteristics of all substances present in thesystem are to be taken into consideration here. In the case of, forexample, skincare emulsions, polar oil components and, for example, UVfilters lead to instability. As well as the emulsifiers, therefore,other stabilizers are also used which, for example, increase theviscosity of the emulsion and/or act as protective colloid.

Emulsions are an important type of product in the field of cosmeticand/or dermatological preparations.

Cosmetic preparations are essentially used for skin care. The main aimof skin care in the cosmetics sense is to strengthen or rebuild theskin's natural function as a barrier against environmental influences(e.g. dirt, chemicals, microorganisms) and against the loss ofendogenous substances (e.g. water, natural fats, electrolytes). If thisfunction becomes impaired, increased resorption of toxic or allergenicsubstances or attack by microorganisms may result, leading to toxic orallergic skin reactions.

Another aim of skin care is to compensate for the loss by the skin oflipids and water caused by daily washing. This is particularly importantif the natural regeneration ability is inadequate. Furthermore, skincareproducts should protect against environmental influences, in particularagainst sun and wind, and delay skin ageing.

Cosmetic preparations are also used as deodorants. Such formulations areused to control body odour, which is produced when fresh perspiration,which is in itself odourless, is decomposed by microorganisms.

Medicinal topical compositions usually comprise one or more medicamentsin an effective concentration. For the sake of simplicity, in order todistinguish clearly between cosmetic and medicinal use and correspondingproducts, reference is made to the legal provisions in the FederalRepublic of Germany (e.g. Cosmetics Directive, Foods and Drugs Act).

The use of customary emulsifiers in cosmetic or dermatologicalpreparations is in itself acceptable. Nevertheless, emulsifiers, likeultimately any chemical substance, may in certain circumstances causeallergic reactions or reactions based on oversensitivity of the user.

For example, it is known that certain light dermatoses are triggered bycertain emulsifiers, but also by various fats and simultaneous exposureto sunlight. Such light dermatoses are also called “Mallorca acne”.There has thus been no lack of attempts to reduce the amount ofcustomary emulsifiers to a minimum, in the ideal case even to zero.

A reduction in the required amount of emulsifier can, for example, beachieved by taking advantage of the fact that very finely divided solidparticles have an additional stabilizing action. The solid substanceaccumulates at the oil/water phase boundary in the form of a layer, as aresult of which coalescence of the disperse phases is prevented. It isnot the chemical properties of the solid particles which are offundamental importance here, but the surface properties.

Around 1910, Pickering prepared paraffin/water emulsions which werestabilized merely by the addition of various solids, such as basiccopper sulphate, basic iron sulphate or other metal sulphates. This typeof emulsion is thus also referred to as a Pickering emulsion.

The original forms of Pickering emulsions initially surfaced, as itwere, as undesired secondary effects in a variety of industrialprocesses, such as, for example, in secondary oil recovery, theextraction of bitumen from tar sand and other separation processesinvolving two immiscible liquids and fine, dispersed solid particles.These are generally W/O emulsions which are stabilized by mineralsolids. Accordingly, investigation of corresponding systems, such as,for example, the oil/water/soot or oil/water/slate dust systems wasinitially the focus of research activity.

Basic experiments have shown that one characteristic of a Pickeringemulsion is that the solid particles are arranged at the interfacebetween the two liquid phases, where they form, as it were, a mechanicalbarrier against the combining of the liquid droplets.

It is a relatively new technical development to use Pickering emulsionsas a base for cosmetic or dermatological preparations.

One way of achieving solids stabilization in the sense of a pickeringemulsion in a cosmetic or dermatological preparation is, according toMay-Alert (Pharmazie in unserer Zeit [Pharmacy in our time], Vol. 15,1986, No. 1, 1-7) for example, to use emulsifier mixtures which compriseboth anionic and cationic surfactants. Since mixing anionic and cationicsurfactants always results in the precipitation of insoluble,electroneutral compounds, deliberate precipitation of these neutralsurfactants in the oil/water interface makes it possible to achieveadditional solids stabilization.

European Laid-open Specification 0 686 391, moreover, describes“emulsions” of the water-in-oil type which are free from surface-activesubstances and are stabilized only by solids. Stabilization is achievedhere using spherical polyalkylsilsesquioxane particles which have adiameter of from 100 nm up to 20 μm, which are added to the oil phaseand thicken it. This type of preparation can therefore also be referredto as oil gels (also: oleogels), into which water can be stablydispersed.

Pickering emulsions are stabilized by the use of suitable solids orpigments. However, the preparations of the prior art generally have thedisadvantage that they are limited to a narrow field of application or arestricted choice of raw materials since they can only be stablyformulated in this manner. For many areas of cosmetics (e.g. for thefield of face care), Pickering emulsions of the prior art haveunsatisfactory cosmetic properties.

The object was therefore to remedy the disadvantages of the prior art.In particular, the intention was to provide cosmetic and dermatologicalbases for cosmetic and dermatological preparations which arecharacterized by good skin tolerability.

In addition, an object of the present invention was to provide productswith the widest possible variety of applications. For example, theintention was to provide bases for preparation forms such as cleansingemulsions, facecare and bodycare preparations or deodorants, but alsodistinctly medicinal-pharmaceutical presentations, for examplepreparations against acne and other skin conditions.

It was surprising and in no way predictable by the person skilled in theart that Pickering emulsions, which are finely disperse systems of thewater-in-oil type, comprising

(1) an oil phase,

(2) a water phase,

(3) at least one type of microfine particles which

a) have an average particle size of less than 200 nm, which

b) display both hydrophilic and lipophilic properties, i.e. which haveamphiphilic character, and are dispersible both in water and in oil andwhich

c) have optionally been coated on the surface,

(4) at least one hydrocolloid and

(5) at most 0.5% by weight of one or more emulsifiers, overcome thedisadvantages of the prior art.

According to the invention, it is particularly advantageous if thepreparations comprise significantly less than 0.5% by weight of one ormore emulsifiers. Very particular preference is given to preparationsaccording to the invention which are entirely free from emulsifiers inthe traditional sense.

The preparations according to the invention are extremely satisfactorypreparations in every respect which have considerably higher stabilitycompared with traditional Pickering emulsions and are therefore suitablein particular to serve as bases for preparation forms having diverseapplication purposes. W/O Pickering emulsions within the meaning of thepresent invention are, surprisingly, markedly stable.

In addition, the preparations according to the invention arecharacterized by excellent skin tolerability. In addition, it wassurprising that preparations according to the invention, which are inthe form of a sunscreen, exhibit higher effectiveness than customarysunscreen formulations.

While preparations of the prior art having a pigment content of aslittle as 1% by weight produce a dull feel following their applicationto the skin, which increases further with higher pigment concentrations,the preparations according to the invention, surprisingly, do not leavea dry or dull impression on the skin, but on the contrary exhibitexcellent cosmetic properties.

Although the prior art recognizes, in addition to Pickering emulsions,emulsifier-free, finely disperse cosmetic or dermatologicalpreparations, which are generally referred to as hydrodispersions andwhich are dispersions of a liquid, semisolid or solid inner(discontinuous) lipid phase in an outer aqueous (continuous) phase,these preparations are oil-in-water formulations.

The prior art was therefore unable to point the way to the presentinvention.

W/O Pickering emulsions for the purposes of the present invention areavailable by dispersing amphiphilic particles suitable for thepreparation of W/O Pickering emulsions and which are in accordance withthe invention into the fatty phase.

“Hydrocolloid” is the technical abbreviation for the more correct term“hydrophilic colloid”. Hydrocolloids are macromolecules which have alargely linear structure and have intermolecular forces of interaction,which permit secondary and primary valence bonds between the individualmolecules and thus the formation of a reticular-structure. Some arewater-soluble natural or synthetic polymers which, in aqueous systems,form gels or viscous solutions. They increase the viscosity of the waterby either binding water molecules (hydration) or else by absorbing andencapsulating the water into their interwoven macromolecules, at thesame time restricting the mobility of the water.

The group of hydrocolloids can be divided as follows into:

organic, natural compounds, such as, for example, agar agar, carrageen,tragacanth, gum arabic, alginates, pectins, polyoses, guar gum, carobbean flour, starch, dextrins, gelatins, casein,

organic, modified natural substances, such as, for example,carboxymethylcellulose and other cellulose ethers, hydroxyethyl and-propylcellulose and the like,

organic, completely synthetic compounds, such as, for example,polyacrylic and polymethacrylic compounds, vinyl polymers,polycarboxylic acids, polyethers, polyimines, polyamides,

inorganic compounds, such as, for example, polysilicic acids, clayminerals such as montmorillonites, zeolites, silicas.

Examples of hydrocolloids which are preferred according to the inventionare methylcelluloses, which -is the name for the methyl ethers ofcellulose. They are characterized by the following structural formula

in which R may be a hydrogen or a methyl group.

Particularly advantageous for the purposes of the present invention arethe cellulose mixed ethers, which are generally likewise referred to asmethylcelluloses, which contain, in addition to a dominating content ofmethyl groups, also 2-hydroxyethyl, 2-hydroxypropyl or 2-hydroxybutylgroups. Particular preference is given to(hydroxypropyl)methylcelluloses, for example those available under thetrade name Methocel E4M from Dow Chemical Comp.

Also advantageous according to the invention is sodiumcarboxymethylcellulose, the sodium salt of the glycolic ether ofcellulose, for which R in structural formula I can be a hydrogen and/orCH₂—COONa. Particular preference is given to the sodiumcarboxymethylcellulose available under the trade name Natrosol Plus 330CS from Aqualon and also referred to as cellulose gum.

Also preferred for the purposes of the present invention is xanthan (CASNo. 11138-66-2), also called xanthan gum, which is an anionicheteropolysaccharide, which is generally formed by fermentation frommaize sugar and is isolated as potassium salt. It is produced fromXanthomonas campestris and some other species under aerobic conditionswith a molecular weight of from 2×10⁶ to 24×10⁶. Xanthan is formed froma chain having β-1,4-bonded glucose (cellulose) with side chains. Thestructure of the subgroups (“repeat units”) consists of glucose,mannose, glucuronic acid, acetate and pyruvate.

Other hydrocolloids which are advantageous according to the inventionare polymers of acrylic acid, in particular those which are chosen fromthe group of carbomers or Carbopols (Carbopol® is actually a registeredtrade mark of the B. F. Goodrich Company). Carbopols are compounds ofthe general structural formula

whose molecular weight can be between about 400,000 and more than4,000,000. The group of Carbopols also includes acrylate-alkyl acrylatecopolymers, for example those characterized by the following structure:

where R′ is a long-chain alkyl radical and x and y are numbers whichsymbolize the respective stoichiometric content of each comonomer. TheseCarbopols, too, are also advantageous for the purposes of the presentinvention.

Examples of advantageous Carbopols are the grades 907, 910, 934, 940,941, 951, 954, 980, 981, 1342, 1382, 2984 and 5984, it being possiblefor these compounds to be present individually or in any combinationwith one another. Particular preference is given to Carbopol 981, 1382and 5984 (either individually or in combination with otherhydrocolloids).

Also advantageous for the purposes of the present invention are thecopolymers, comparable with the acrylate-alkyl acrylate copolymers, ofC₁₀₋₃₀-alkyl acrylates and one or more monomers of acrylic acid, ofmethacrylic acid or esters thereof. The INCI name for such compounds is“Acrylates/C 10-30 Alkyl Acrylate Crosspolymer”. Particularlyadvantageous are those available under the trade names Pemulen TR1 andPemulen TR2 from B. F. Goodrich Company.

The total amount of one or more hydrocolloids in the finished cosmeticor dermatological W/O-Pickering emulsions is advantageously chosen to beless than 1.0% by weight, preferably between 0.01 and 0.5% by weight,based on the total weight of the preparations.

It is also advantageous, although not obligatory, for the Pickeringemulsions according to the invention to comprise other auxiliaries whichcan additionally increase the stability of these preparations, forexample substances which are chosen from the group of waxes and/or oilthickeners, and of electrolytes.

It is also advantageous for the Pickering emulsions according to theinvention to comprise auxiliaries which can contribute to reducing orpreventing a dull or dry feel on the skin following their application,where it is possible that the main purpose of these substances is adifferent one. Preferably, these substances are, for example, chosenfrom the group of unsymmetrically substituted s-triazine derivatives,cyclodextrins, film formers and polymeric moisturizers, it beingpossible for these substances to be present either individually or in amixture.

The cosmetic properties of the Pickering emulsions according to theinvention can additionally, for example, be further improved by alsousing oils in the oil phase which have a viscosity of less than 30mPa.s, in particular of less than 20 mPa.s (determined using a rheometerfrom Contraves (Rheomat 108E) at a shear gradient of 500/s and atemperature of 25° C.).

Microfine Particles

The amphiphilic character of the microfine particles according to theinvention is evident, for example, from the fact that they aredispersible both in water and in oil.

It is advantageous to choose the average particle diameter of theparticles used to be between 1 nm and 200 nm, particularlyadvantageously between 5 nm and 100 nm.

It is also advantageous to choose the concentration of all amphiphilicparticles according to the invention to be greater than 0.1% by weight,particularly advantageously between 0. 1% by weight and 30% by weight,based on the total weight of the preparations.

For the purposes of the present invention, advantageous particles areall those which are suitable for stabilizing Pickering W/O emulsions. Itis essentially insignificant for the present invention in which of thepotentially naturally occurring modifications the particles are present.

To stabilize the Pickering emulsions, preference is given to usinguntreated, virtually pure pigment particles, in particular those whichcan be used as dyes in the food industry and/or as absorbers of UVradiation in sunscreens. Examples of advantageous pigments are the zincoxide pigments available from Merck which are available under the tradenames Zinkoxid neutral from Haarmann & Reimer or NanoX from HarcrosChemical Group.

For the purposes of the present invention, Pickering emulsions arelikewise advantageously stabilized by inorganic pigments which have beensurface-treated (“coated”) to repel water, where at the same time theintention is to form or retain the amphiphilic character. Thissurface-treatment can consist in providing the pigments with a thinhydrophobic layer by processes known per se.

One such process, which is described below using titanium dioxide as anexample, consists in, for example, producing the hydrophobic surfacelayer according to the following reaction

n TiO₂+m(RO)₃Si—R′→ n TiO₂(surf.).

n and m are arbitrary stoichiometric parameters, and R and R′ are thedesired organic radicals. Particularly advantageous are TiO₂ pigments,for example those coated with aluminium stearate, available under thetrade name MT 100 T from TAYCA.

A further advantageous coating of the inorganic pigments consists ofdimethylpolysiloxane (also: dimethicone), a mixture of completelymethylated, linear siloxane polymers which are terminally blocked withtrimethylsiloxy units. For the purposes of the present invention,particularly advantageous pigments are zinc oxide pigments which arecoated in this way.

Also advantageous is a coating of the inorganic pigments with a mixtureof dimethylpolysiloxane, in particular dimethylpolysiloxane having anaverage chain length of from 200 to 350 dimethylsiloxane units, andsilica gel, which is also referred to as simethicone. It is particularlyadvantageous if the inorganic pigments have been additionally coatedwith aluminium hydroxide or hydrated aluminium oxide (also alumina, CASNo.: 1333-84-2). Particularly advantageous are titanium dioxides whichhave been coated with simethicone and alumina, it being possible for thecoating to also comprise water. One example thereof is the titaniumdioxide available under the trade name Eusolex T2000 from Merck.

For the purposes of the present invention it is also advantageous to usea mixture of different pigment types either within a crystal, forexample as mixed iron oxide, or by combination of two or more pigmenttypes within a preparation.

The Pickering emulsions are also preferably stabilized by boron nitrideparticles, for example by the boron nitrides listed below:

Trade name Available from Boron Nitride Powder Advanced Ceramics BoronNitride Powder Sintec Keramik Ceram Blanche Kawasaki HCST Boron NitrideStark Très BN ® Carborundum Wacker-Bornitrid BNP Wacker-Chemie

It is advantageous to choose the average particle diameter of the boronnitride particles used to be less than 20 μm, particularlyadvantageously less than 15 μm. For the purposes of the presentinvention, Pickering emulsions are likewise advantageously stabilized byboron nitride particles which have been surface-treated (“coated”) torepel water, where at the same time the intention is to form or retainthe amphiphilic character.

An advantageous coating of the boron nitride particles consists ofdimethylpolysiloxane (dimethicone). The boron nitride particles treatedwith dimethicone and available from Carborundum under the trade nameTres BN® UHP 1106 are advantageous, for example.

Also advantageous is a coating of the boron nitride particles withpolymethylhydrogensiloxane, a linear polysiloxane which is also referredto as methicone. Advantageous boron nitride particles treated withmethicone are, for example, those available from Carborundum under thetrade name Tres BN® UHP 1107.

It is also advantageous to stabilize the Pickering emulsions accordingto the invention using microfine polymer particles.

For the purposes of the present invention, examples of advantageousmicrofine polymer particles are polycarbonates, polyethers,polyethylenes, polypropylenes, polyvinyl chloride, polystyrene,polyamides, polyacrylates and the like.

Advantageous according to the invention are, for example, microfinepolyamide particles which are available under the trade name SP-500 fromTORAY. Also advantageous are polyamide 6 (also: nylon 6) and polyamide12 (also: nylon 12) particles. Polyamide 6 is the polyamide formed fromε-aminocaproic acid (6-aminohexanoic acid) or ε-caprolactam[poly(ε-caprolactam)], and polyamide 12 is a poly(c-laurolactam) fromε-Iaurolactam. For the purposes of the present invention, Orgasol® 1002(polyamide 6) and Orgasol® 2002 (polyamide 12) from ELF ATOCHEM, forexample, are advantageous.

Other advantageous polymer particles are microfine polymethacrylates.Such particles are available, for example, under the trade namePOLYTRAP® from DOW CHEMICAL.

It is particularly advantageous, but not obligatory, if the microfinepolymer particles used have been surface-coated. This surface-treatmentcan consist in providing the pigments with a thin hydrophilic layer byprocesses known per se. Advantageous coatings consist, for example, ofTiO₂, ZrO₂ or also other polymers, such as, for example, polymethylmethacrylate.

Particularly advantageous microfine polymer particles for the purposesof the present invention are also obtainable by the process, describedin U.S. Pat. Specification No. 4,898,913, for the hydrophilic coating ofhydrophobic polymer particles.

It is advantageous to choose the average particle diameter of themicrofine polymer particles used to be less than 100 μm, particularlyadvantageously less than 50 μm. In this connection, it is essentiallyinsignificant in which form (platelets, rods, spherules, etc.) thepolymer particles used are present.

In addition, it is advantageous to stabilize the Pickering emulsionsaccording to the invention using modified polysaccharides.

For the purposes of the present invention, modified polysaccharides are,for example, obtainable by reaction of starch with mono-, bi- orpolyfunctional reagents or oxidizing agents in reactions which proceedin a largely polymer-analogous manner.

Such reactions are based essentially on modifications of the hydroxylgroups of the polyglucans by etherification, esterification or selectiveoxidation. This produces, for example, so-called starch ethers andstarch esters of the general structural formula

in which R can, for example, be a hydrogen and/or an alkyl and/or anaralkyl radical (in the case of starch ethers) or a hydrogen and/or anorganic and/or inorganic acid radical (in the case of starch esters).Starch ethers and starch esters are advantageous, modifiedpolysaccharides for the purposes of the present invention.

Particularly advantageous starch ethers are, for example, those whichare obtainable by etherification of starch withtetramethylolacetylenediurea and which are referred to asnon-mucilaginous starch (nonswelling starch).

Also particularly advantageous are starch esters and salts thereof, forexample the sodium and/or aluminium salts of half-esters of starch whichhave low degrees of substitution, in particular sodium starch n-octenylsuccinate of the structural formula (II) in which R is characterized bythe following structure

and which is available, for example, under the trade name Amiogum® 23from CERESTAR, and aluminium starch octenyl succinates, in particularthose available under the trade names Dry Flo® Elite LL and Dry Flo® PCfrom CERESTAR.

It is advantageous to choose the average particle diameter of themodified polysaccharide used to be less than 20 μm, particularlyadvantageously less than 15 μm.

The list of given modified polysaccharides which are able to stabilizePickering emulsions according to the invention is of course not intendedto be limiting. For the purposes of the present invention, modifiedpolysaccharides are obtainable in a large number of ways known per se,both of a chemical and a physical nature.

Also particularly advantageous for stabilizing W/O Pickering emulsionsare magnesium silicates (also: talc), for example those available underthe trade name Talkum Micron from Grolmann.

The water phase proportion in the W/O Pickering emulsions according tothe invention is preferably chosen from the range of from 0.5 to 75% byweight, based on the total weight of the formulations.

It is also advantageous, but not obligatory, to combine the microfineparticles according to the invention with other amphiphilic particleswhich may or may not also be able to contribute to the stabilization ofthe Pickering emulsions.

Such particles are, for example, titanium dioxide pigments which havebeen coated with octylsilanol, and/or silicon dioxide particles whichhave been surface-treated to repel water. Suitable silicon dioxideparticles are, for example, spherical polyalkylsilsesquioxane particles,as mentioned in European Laid-open Specification 0 686 391. Suchpolyalkylsilsesquioxane particles are available, for example, under thetrade names Aerosil R972 and Aerosil 200V from Degussa. Suitabletitanium dioxide particles are available under the trade name T805, alsofrom Degussa.

Oil Phase

The oil phase of the O/W emulsions according to the invention isadvantageously chosen from the group of polar oils, for example from thegroup of lecithins and fatty acid triglycerides, namely the triglycerolesters of saturated and/or unsaturated, branched and/or unbranchedalkane carboxylic acids having a chain length of from 8 to 24, inparticular from 12 to 18, carbon atoms. The fatty acid triglycerides canbe advantageously chosen, for example, from the group of synthetic,semisynthetic and natural oils, such as, for example, olive oil,sunflower oil, soybean oil, peanut oil, rapeseed oil, almond oil, palmoil, coconut oil, castor oil, wheatgerm oil, grapeseed oil, thistle oil,evening primrose oil, macadamia nut oil and the like.

For the purposes of the present invention, other advantageous polar oilcomponents can also be chosen from the group of esters of saturatedand/or unsaturated, branched and/or unbranched alkane carboxylic acidshaving a chain length of from 3 to 30 carbon atoms and saturated and/orunsaturated, branched and/or unbranched alcohols having a chain lengthof from 3 to 30 carbon atoms, and from the group of esters of aromaticcarboxylic acids and saturated and/or unsaturated, branched and/orunbranched alcohols having a chain length of from 3 to 30 carbon atoms.Such ester oils can then advantageously be chosen from the groupconsisting of isopropyl myristate, isopropyl palmitate, isopropylstearate, isopropyl oleate, n-butyl stearate, n-hexyl laurate, n-decyloleate, isooctyl stearate, isononyl stearate, isononyl isononanoate,2-ethylhexyl palmitate, 2-ethylhexyl laurate, 2-hexyldecyl stearate,2-octyldodecyl palmitate, oleyl oleate, oleyl erucate, erucyl oleate,erucyl erucate, and synthetic, semisynthetic and natural mixtures ofsuch esters, such as, for example, jojoba oil.

In addition, the oil phase can advantageously be chosen from the groupof dialkyl ethers, the group of saturated or unsaturated, branched orunbranched alcohols. It is particularly advantageous for the oil phaseof the O/W emulsions according to the invention to have a content ofC₁₂₋₁₅-alkyl benzoate or to consist entirely of this.

Any desired mixtures of such oil and wax components can also be usedadvantageously for the purposes of the present invention. In someinstances, it can also be advantageous to use waxes, for example cetylpalmitate, as the sole lipid component of the oil phase.

In addition, the oil phase of the O/W emulsions according to theinvention can likewise advantageously, but not obligatorily, alsocomprise nonpolar oils, for example those which are chosen from thegroup of branched and unbranched hydrocarbons and hydrocarbon waxes, inparticular vaseline (petrolatum), paraffin oil, squalane and squalene,polyolefins and hydrogenated polyisobutenes. Of the polyolefins,polydecenes are the preferred substances.

The oil phase can advantageously also have a content of cyclic or linearsilicone oils or consist entirely of such oils, although it is preferredto use an additional content of other oil phase components apart fromthe silicone oil or the silicone oils.

Advantageously, cyclomethicone (octamethylcyclotetrasiloxane) is used assilicone oil to be used according to the invention. However, othersilicone oils are also to be used advantageously for the purposes of thepresent invention, for example hexamethylcyclotrisiloxane,polydimethylsiloxane, poly(methylphenylsiloxane).

The Pickering emulsions according to the invention can be used as basesfor cosmetic or dermatological formulations. These can have thecustomary composition and be used, for example, for the treatment andcare of the skin, as lipcare products, as deodorant products and asmake-up products or make-up remover products in decorative cosmetics oras light protection preparations. For use, the cosmetic anddermatological preparations according to the invention are applied tothe skin in sufficient amounts in the manner customary for cosmetics.

Accordingly, for the purposes of the present invention, cosmetic ortopical dermatological compositions may, depending on their structure,be used, for example, as skin-protection creams, cleansing milks,sunscreen lotions, nourishing creams, day creams or night creams, etc.In some instances, it is possible and advantageous to use thecompositions according to the invention as bases for pharmaceuticalformulations.

The cosmetic and dermatological preparations according to the inventioncan comprise cosmetic auxiliaries, as are customarily used in suchpreparations, e.g. preservatives, bactericides, perfumes, antifoams,dyes, pigments which have a colouring effect, further thickeners,emollients, moisturizers and/or humectants, fats, oils, waxes and othercustomary constituents of a cosmetic or dermatological formulation, suchas alcohols, polyols, polymers, foam stabilizers, electrolytes, organicsolvents or silicone derivatives.

In particular, the Pickering emulsions according to the invention mayalso comprise antioxidants. According to the invention, favourableantioxidants which can be used are any antioxidants suitable orconventional for cosmetic and/or dermatological applications.

The antioxidants are advantageously chosen from the group consisting ofamino acids (e.g. glycine, histidine, tyrosine, tryptophan) andderivatives thereof, imidazoles, (e.g. urocanic acid) and derivativesthereof, peptides, such as D,L-camosine, D-carnosine, L-camosine andderivatives thereof (e.g. anserine), carotenoids, carotenes (e.g.α-carotene, carotene, lycopene) and derivatives thereof, chlorogenicacid and derivatives thereof, lipoic acid and derivatives thereof (e.g.dihydrolipoic acid), aurothioglucose, propylthiouracil and other thiols(e.g. thioredoxin, glutathione, cysteine, cystine, cystamine and theglycosyl, N-acetyl, methyl, ethyl, propyl, amyl, butyl and lauryl,palmitoyl, oleyl, γ-linoleyl, cholesteryl and glyceryl esters thereof)and the salts thereof, dilauryl thiodipropionate, distearylthiodipropionate, thiodipropionic acid and derivatives thereof (esters,ethers, peptides, lipids, nucleotides, nucleosides and salts) andsulphoximine compounds (e.g. buthionine sulphoximines, homocysteinesulphoximine, buthionine sulphones, penta-, hexa-, heptathioninesulphoximine) in very low tolerated doses (e.g. pmol to μmol/kg), andalso (metal) chelating agents (e.g. α-hydroxy fatty acids, palmiticacid, phytic acid, lactoferrin), α-hydroxy acids (e.g. citric acid,lactic acid, malic acid), humic acid, bile acid, bile extracts,bilirubin, biliverdin, EDTA, EGTA and derivatives thereof, unsaturatedfatty acids and derivatives thereof (e.g. γ-linolenic acid, linoleicacid, oleic acid), folic acid and derivatives thereof, ubiquinone andubiquinol and derivatives thereof, vitamin C and derivatives (e.g.ascorbyl palmitate, Mg ascorbyl phosphate, ascorbyl acetate),tocopherols and derivatives (e.g. vitamin E acetate), vitamin A andderivatives (vitamin A palmitate) and coniferyl benzoate of benzoinresin, rutinic acid and derivatives thereof, c-glycosylrutin, ferulicacid, furfurylideneglucitol, carnosine, butylated hydroxytoluene,butylated hydroxyanisole, nordihydroguaiac acid, nordihydroguaiareticacid, trihydroxybutyrophenone, uric acid and derivatives thereof,mannose and derivatives thereof, zinc and derivatives thereof (e.g. ZnO,ZnSO₄), selenium and its derivatives (e.g. selenomethionine), stilbenesand their derivatives (e.g. stilbene oxide, trans-stilbene oxide), andthe derivatives (salts, esters, ethers, sugars, nucleotides,nucleosides, peptides and lipids) of said active substances which aresuitable according to the invention.

The amount of the abovementioned antioxidants (one or more compounds) inthe preparations according to the invention is preferably from 0.001 to30% by weight, particularly preferably from 0.05 to 20% by weight, inparticular 0.1 to 10% by weight, based on the total weight of thepreparation.

If vitamin E and/or derivatives thereof are used as the antioxidant orantioxidants, their arespective concentrations are advantageously chosenfrom the range of 0.001 to 10% by weight, based on the total weight ofthe formulation.

If vitamin A or vitamin A derivatives or carotenes or derivativesthereof are used as the antioxidant or antioxidants, their respectiveconcentrations are advantageously chosen from the range of 0.001-10% byweight, based on the total weight of the formulation.

Cosmetic and dermatological preparations which are in the form of asunscreen are also favourable. These preferably comprise at least oneUV-A filter substance and/or at least one UV-B filter substance and/orat least one further inorganic pigment selected from the groupconsisting of the oxides of iron, zirconium, silicon, manganese,aluminium, cerium and mixtures thereof and also modifications in whichthe oxides are the active agents.

For the purposes of the present invention, it is, however, alsoadvantageous to provide such cosmetic and dermatological preparationswhose main purpose is not protection against sunlight, but whichnevertheless comprise substances which protect against UV. For example,UV-A and UV-B filter substances are commonly incorporated into daycreams.

UV protection substances, like antioxidants and, if desired,preservatives, also represent effective protection of the preparationsthemselves against decay.

The preparations according to the invention can advantageously comprisesubstances which absorb UV radiation in the UV-A and/or UV-B range, thetotal amount of filter substances being, for example, from 0.1% byweight to 30% by weight, preferably from 0.5 to 20% by weight, inparticular from 1.0 to 15.0% by weight, based on the total weight of thepreparations, in order to provide cosmetic preparations which protectthe hair and/or the skin from the whole of ultraviolet radiation. Theycan also be used as sunscreens for hair and skin.

Advantageous UV-A filter substances for the purposes of the presentinvention are dibenzoylmethane derivative, in particular4-(tert-butyl)-4′-methoxydibenzoylmethane (CAS No. 70356-09-1), which issold by Givaudan under the name Parsol® 1789 and by Merck under thetrade name Eusolex® 9020.

Other advantageous UV-A filter substances arephenylene-1,4-bis(2-benzimidazyl)-3,3′-5,5′-tetrasulphonic acid:

and its salts, particularly the corresponding sodium, potassium ortriethanolammonium salts, in particular the bis-sodium salt ofphenylene-1,4-bis(2-benzimidazyl)-3,3′-5,5′-tetrasulphonic acid:

and 1,4-di(2-oxo-10-sulfo-3-bornylidenemethyl)benzene and salts thereof(particularly the corresponding 10-sulfato compounds, in particular thecorresponding sodium, potassium or triethanolammonium salt), which isalso referred to asbenzene-1,4-di(2-oxo-3-bornylidenemethyl-10-sulphonic acid) and ischaracterized by the following structure:

For the purposes of-the present invention, advantageous UV filtersubstances are also so-called broadband filters, i.e. filter substanceswhich absorb both UV-A and UV-B radiation.

Advantageous broadband filters and/or UV-B filter substances are, forexample, bisresorcinyltriazine derivatives having the followingstructure:

where R¹, R² and R³ independently of one another are chosen from thegroup of branched and unbranched alkyl groups having from 1 to 10 carbonatoms, or a single hydrogen atom. Particular preference is given to2,4-bis-{[4-(2-ethylhexyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazineand tris(2-ethylhexyl)4,4′,4″-(1,3,5-triazine-2,4,6-triyltriimino)trisbenzoate, synonym:2,4,6-tris[anilino(p-carbo-2′-ethyl-1′-hexyloxy)]-1,3,5-triazine, whichis marketed by BASF Aktiengesellschaft under the trade name UVINUL® T150.

Other UV filter substances, which have the structural formula

are also advantageous UV filter substances for the purposes of thepresent invention, for example the s-triazine derivatives described inEuropean Laid-open Specification EP 570 838 A1, the chemical structurefor which is given by the generic formula

where

R is a branched or unbranched C₁-C₁₈-alkyl radical, a C₅-C₁₂-cycloalkylradical, optionally substituted with one or more C₁-C₄-alkyl groups,

X is an oxygen atom or an NH group,

R₁ is a branched or unbranched C₁-C₁₈-alkyl radical, a C₅-C₁₂-cycloalkylradical, optionally substituted with one or more C₁-C₄-alkyl groups, ora hydrogen atom, an alkali metal atom, an ammonium group or a group ofthe formula

 in which

A is a branched or unbranched C₁-C₁₈-alkyl radical, a C₅-C₁₂-cycloalkylor aryl radical, optionally substituted with one or more C₁-C₄-alkylgroups,

R₃ is a hydrogen atom or a methyl group,

n is a number from 1 to 10,

R₂ is a branched or unbranched C₁-C₁₈-alkyl radical, a C₅-C₁₂-cycloalkylradical, op2ionally substituted by one or more C₁-C₄-alkyl groups, whenX is the NH group, and

is a branched or unbranched C₁-C₁₈-alkyl radical, a C₅-C₁₂-cycloalkylradical, optionally substituted with one or more C₁-C₄-alkyl groups, ora hydrogen atom, an alkali metal atom, an ammonium group or a group ofthe formula

 in which

A is a branched or unbranched C₁-C₁₈-alkyl radical, a C₅-C₁₂-cycloalkylor aryl radical, optionally substituted with one or more C₁-C₄-alkylgroups,

R₃ is a hydrogen atom or a methyl group,

n is a number from 1 to 10,

when X is an oxygen atom.

An example of such unsymmetrically substituted s-triazines isdioctylbutylamidotriazone.

Other UV filter substances, whose incorporation into cosmetic ordermatological light protection formulations hitherto had problems, arealso known. For example, European Laid-open Specification 775 698describes bisresorcinoltriazine derivatives, the chemical structure forwhich is given by the generic formula

where R₁, R₂ and A₁ represent very different organic radicals.

Also advantageous for the purposes of the present invention are2,4-bis{[4-(2-ethylhexyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazine,2,4-bis{[4-(3-sulfonato)-2-hydroxypropyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazinesodium salt,2,4-bis{[4-(3-(2-propyloxy)-2-hydroxypropyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazine,2,4-bis{[4-(2-ethylhexyloxy)-2-hydroxy]phenyl}-6-[4-(2-methoxyethylcarboxyl)phenylamino]-1,3,5-triazine,2,4-bis{[4-(3-(2-propyloxy)-2-hydroxypropyloxy)-2-hydroxy]phenyl}-6-[4-(2-ethylcarboxyl)phenylamino]-1,3,5-triazine,2,4-bis{[4-(2-ethylhexyloxy)-2-hydroxy]phenyl}-6-(1-methylpyrrol-2-yl)-1,3,5-triaine,2,4-bis{[4-tris(trimethylsiloxysilyipropyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazine,2,4-bis{[4-(2″-methylpropenyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazineand 2,4-bis{[4-(1′,1′,1′,3′,5′,5′,5′-heptamethylsiloxy-2″-methylpropyloxy)-2-hydroxy]phenyl}-6-(4-methoxyphenyl)-1,3,5-triazine.

Another advantageous UV filter for the purposes of the present inventionis2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol),which is characterized by the chemical structural formula

Also advantageous for the purposes of the present invention is2-(2H-benzotriazol-2-yl)-4-methyl-6-[2-methyl-3-[1,3,3,3-tetramethyl-1-[(trimethylsilyl)oxy]disiloxanyl]propyl]phenol(CAS-No.: 155633-54-8) having the INCI name Drometrizole Trisiloxane,which is characterized by the chemical structural formula

The UV-B filters can be oil-soluble or water-soluble. Examples ofadvantageous oil-soluble UV-B filter substances are:

3-benzylidenecamphor derivates, preferably3-(4-methylbenzylidene)camphor, 3-benzylidenecamphor;

4-aminobenzoic acid derivates, preferably 2-ethylhexyl4-(dimethylamino)benzoate, amyl 4-(dimethylamino)benzoate;

2,4,6-trianilino-(p-carbo-2′-ethyl-1′-hexyloxy)-1,3,5-triazine;

Esters of benzalmalonic acid, preferably di(2-ethylhexyl)4-methoxybenzalmalonate;

Esters of cinnamic acid, preferably 2-ethylhexyl 4-methoxycinnamate,isopentyl 4-methoxycinnamate;

Derivates of benzophenone, preferably 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-methoxy-4′-methylbenzophenone,2,2′-dihydroxy-4-methoxybenzophenone

and UV filters bonded to polymers.

Examples of advantageous water-soluble UV-B filter substances are:

Salts of 2-phenylbenzimidazol-5-sulphonic acid, such as its sodium,potassium or triethanolammonium salts, and the sulphonic acid itself;

Sulphonic acid derivates of 3-benzylidenecamphor, such as, for example,4-(2-oxo-3-bornylidenmethyl)benzenesulphonic acid,2-methyl-5-(2-oxo-3-bornylidenemethyl)sulphonic acid and salts thereof.

Another light protection filter substance to be used advantageouslyaccording to the invention is 2-ethylhexyl 2-cyano-3,3-diphenylacrylate(octocrylene), which is available from BASF under the name Uvinul® N 539and is characterized by the following structure:

It can also be of considerable advantage to use polymer-bonded orpolymer UV filter substances in preparations according to the presentinvention, in particular those described in WO-A-92/20690.

In addition, it may in some circumstances be advantageous to incorporateother UV-A and/or UV-B filters according to the invention into cosmeticor dermatological preparations, for example certain salicylic acidderivatives such as 4-isopropylbenzyl salicylate, 2-ethylhexylsalicylate (=octyl salicylate), homomenthyl salicylate.

The list of given UV filters which can be used for the purposes of thepresent invention is of course not intended to be limiting.

Preparations according to the invention can also be advantageously usedas bases for cosmetic deodorants and antiperspirants, so that aparticular embodiment of the present invention relates to Pickeringemulsions as bases for cosmetic deodorants.

Cosmetic deodorants are used to control body odour which arises whenfresh perspiration, which is in itself odourless, is decomposed bymicroorganisms. Customary cosmetic deodorants are based on various modesof action.

In antiperspirants, astringents, mainly aluminium salts, such asaluminium hydroxychloride (aluminium chlorohydrate), reduce theformation of perspiration.

The use of antimicrobial substances in cosmetic deodorants can reducethe bacterial flora of the skin. In an ideal situation, only themicroorganisms which cause the odour should be effectively reduced. Theflow of perspiration itself is not influenced as a result, and in idealcircumstances, only microbial decomposition of perspiration is stoppedtemporarily.

The combination of astringents and antimicrobial active substances inone and the same composition is also common.

All active ingredients common for deodorants or antiperspirants canadvantageously be used, for example odour concealers, such as customaryperfume constituents, odour absorbers, for example the phyllosilicatesdescribed in Laid-open Patent Specification DE 40 09 347, of these inparticular montmorillonite, kaolinite, illite, beidellite, nontronite,saponite, hectorite, bentonite, smectite, and also, for example, zincsalts of ricinoleic acid. Antibacterial agents are also suitable to beincorporated into the novel W/O emulsion sticks. Advantageous substancesare, for example, 2,4,4′-trichloro-2′-hydroxy diphenyl ether (Irgasan),1,6-di(4-chlorophenylbiguanido)hexane (chlorhexidine),3,4,4′-trichlorocarbanilide, quatemary ammonium compounds, oil ofcloves, mint oil, thyme oil, triethyl citrate, farnesol(3,7,11-trimethyl-2,6,10-dodecatrien-1-ol) and also the activeingredients or active ingredient combinations described in the Laid-openPatent Specifications DE-A-37 40 186, DE-A-39 38 140, DE-A-42 04 321,DE-A-42 29 707, DE-A-43 09 372, DE-A-44 11 664, DE-A-195 41 967,DE-A-195 43 695, DE-A-195 43 696, DE-A-195 47 160, DE-A-196 02 108,DE-A-196 02 110, DE-A-196 02 111, DE-A-196 31 003, DE-A-196 31 004 andDE-A-196 34 019, and the Patent Specifications DE-42 29 737, DE-42 37081, DE43 24 219, DE-44 29 467, DE-44 23 410 and DE-195 16 705. Sodiumhydrogencarbonate can also be used advantageously.

The list of specified active ingredients and active ingredientcombinations is of course not intended to be limiting.

The amount of antiperspirant active ingredients or deodorants (one ormore compounds) in the preparations is preferably from 0.01 to 30% byweight, particularly preferably from 0.1 to 20% by weight, in particular1-10% by weight, based on the total weight of the preparation.

The examples below serve to illustrate the present invention withoutlimiting it. The numerical values in the examples are percentages byweight, based on the total weight of the respective preparations.

EXAMPLES

1 2 3 W/O W/O W/O Titanium dioxide (Eusolex T2000) 2 4 6 Zinc oxide 5 4Titanium dioxide (Titandioxid T805) 2 Silica (Aerosil R972) 1 0.5 Talc(Talkum Micron) 0.5 Boron nitride 2 Hydroxystearyl hydroxystearate(Elfacos 2 2 C26) C₂₀₋₄₀-alkyl stearate (Kesterwachs K82) 1 1C₁₆₋₃₈-alkylhydroxystearolyl stearate 2 (Kesterwachs k80P) Behenoxydimethicone (Abil Wax 2440) 5 Polyisobutene (Rewopal PIB 1000) 5Caprylic/capric triglyceride 5 5 5 Octyldodecanol 5 5 Mineral oil 10Butylene glycol caprylate/caprate 10 10 C₁₂₋₁₅-alkyl benzoate 10 10 10Dimethicone 2 3 Hydrogenated polyisobutene (Polysynian) 2Methylbenzylidenecamphor 3 Octyltriazone 1 Dibenzoylmethane 2Dioctylbutamidotriazone (UVASORB HEB) 2 Preservative 0.5 0.5 0.5Glycerol 5 10 3 Biosaccharide gel (Fucogel 1000) 5 NaCl 1 1 MgSO₄ 0.5Phenylbenzimidazolesulphonic acid 1 Carbomer (Carbopol 981) 0.1C₁₀₋₃₀-alkyl acrylate crosspolymer (Pemulen 0.01 TR1) Xanthan gum 0.05Sodium carboxylmethylcellulose (Natrosol 0.05 0.01 Plus 330 CS) NaOH 45%strength solution in water 0.3 0.01 EDTA solution 1 Water ad 100 ad 100ad 100

What is claimed is:
 1. Pickering emulsions, which are finely disperse water-in-oil systems, comprising (1) an oil phase, (2) a water phase, (3) microfine particles which a) have an average particle size of less than 200 nm, which b) display both hydrophilic and lipophilic properties, and are dispersible both in water and in oil and which c) have optionally been coated on the surface, (4) at least one hydrocolloid and (5) at most 0.5% by weight of one or more emulsifiers.
 2. Pickering emulsions according to claim 1, wherein said emulsions are emulsifier-free.
 3. Pickering emulsions according to claim 1, wherein the content of the particles used is between 0.1% by weight and 30% by weight, based on the total weight of the preparations.
 4. Pickering emulsions according to claim 1, wherein the particle diameter of the particles used is between 5 nm and 100 nm.
 5. Pickering emulsions according to claim 1, wherein the microfine particles used are selected from the group cinsisting of amphiphilic metal oxides, microfine polymer particles, modified polysaccharides and mixtures thereof.
 6. Pickering emulsions according to claim 1, wherein the particles used have been surface-treated to repel water and the amphiphilic character of the particles is formed or retained. 